1. Field of the Invention
This invention relates to a wheel hub for a bicycle, more particularly to a wheel hub which includes a hub shell rotatably supported on a hub shaft, and a screw-threaded cylinder interconnecting detachably a driven cylinder and the hub shell.
2. Description of the Related Art
A conventional quick-release wheel hub for a bicycle, such as that disclosed in U.S. Pat. No. 4,580,670, includes a hub shell which is supported rotatably on a hub shaft, and a driven cylinder of a freewheel which is fitted and fixed non-rotatably to the hub shaft at one lateral side. The hub shell has an internally threaded portion. A screw-threaded cylinder has an externally threaded portion at one end for threaded engagement with the internally threaded portion, and a projection at the other end for engaging one end of the driven cylinder, thereby fixing the driven cylinder to the hub shell. However, when the driven cylinder is removed from the hub shell for replacement, the screw-threaded cylinder must be removed from the hub shell, and can be easily misplaced.
The object of the present invention is to provide a wheel hub in which a screw-threaded cylinder can be kept in an axial hole in a hub shell even after a driven cylinder has been removed from the hub shell, thereby preventing misplacement of the screw-threaded cylinder.
According to this invention, the wheel hub includes a hub shell which is adapted to be rotatably supported on an axle, and which has first and second lateral ends that are disposed opposite to each other in an axial direction, and an inner peripheral wall that extends in the axial direction around the axle to communicate the first and second lateral ends. The inner peripheral wall includes first to fifth wall segments defining different diameters. A driven cylinder is adapted to be sleeved rotatably on the axle, and has an engaging portion of such a dimension so as to be fitted to the first wall segment in the axial direction and to be non-rotatable relative to the hub shell. The engaging portion extends in the axial direction, and has an end wall, and an internally threaded portion which extends from the end wall inwardly and in the axial direction. A driving cylinder is rotatably mounted on the driven cylinder, and is adapted to be provided with a sprocket wheel. A screw-threaded cylinder can enter the second wall segment via the second lateral end, and includes a shank and a head. The shank can be fitted to the third wall segment, and extends in the axial direction to have a length longer than that of the third wall segment so as to form a projecting portion that extends beyond the third wall segment to the first wall segment. The projecting portion is provided with an externally threaded portion which engages threadedly the internally threaded portion when the engaging portion of the driven cylinder is fitted to the first wall segment. The head is disposed opposite to the shank in the axial direction, and has an outer surrounding wall which defines a diameter that is slightly smaller than the diameter of the fourth wall segment and larger than the diameter of the third wall segment. A shoulder is formed between the head and the shank, and is restrained by another shoulder between the third and fourth wall segments from moving toward the first lateral end during the threaded engagement of the externally threaded portion with the internally threaded portion. A resilient member is disposed on the outer surrounding wall of the head, and is deformable in a radial direction relative to the axle. During insertion of the screw-threaded cylinder into the axial hole via the second lateral end, when the head is forced into the fifth wall segment, the resilient member is deformed in the radial direction by the fifth wall segment so as to permit the head to slip into the fourth wall segment, where the resilient member is in contact with and is rotatable relative to the fourth wall segment.